A fuel monitoring system for automatically monitoring a fuel transfer in an aircraft fuel system, the fuel system including a plurality of fuel tanks, the fuel monitoring system comprises a fuel quantity sensor arranged to measure the quantity of fuel in a first fuel tank and a data processor arranged to receive a fuel quantity measurement from the sensor, wherein in response to receiving a command to transfer fuel from the first fuel tank to one or more further fuel tanks the data processor is arranged to determine the rate of change of fuel quantity in the first tank from the received fuel quantity measurement and if the rate of change of fuel quantity is less than a threshold value and the received fuel quantity measurement is greater than an expected value then the data processor is further arranged to provide an output indicating that the commanded fuel transfer has failed.